Materials and device properties of ultra-thin 6.0 /spl Aring/ In/sub x/Al/sub 1-x/As graded buffer layers and HBTS

The rapid kinetics of strain relaxation in In/sub x/Al/sub 1-x/As graded buffer layers (GBLs) was exploited to produce thin (0.21 /spl mu/m-0.90 /spl mu/m) buffer layers graded from the InP substrate to 6.0 /spl Aring/. The layers were fully relaxed, with a cross-hatched surface roughness of 4 nm, and threading dislocation densities of about 10/sup 8/ cm/sup -2/ for the thinnest buffer and 10/sup 6/ cm/sup -2/ for the 0.45 and 0.90 /spl mu/m GBL structures. Identical HBT structures were grown on each of these buffers. The current gain was at least 60 with low reverse leakage currents.